The present invention relates generally to microstrip antennas, and more particularly to a microstrip antenna system which combines a two-port, rectangular patch microstrip antenna with a signal processing system which enables the patch antenna to transmit and receive two circularly polarized waves of opposite senses simultaneously.
Microstrip antennas, despite their limited bandwidths, can be designed to perform many functions, sometimes even simultaneously. For example, a single element can easily be made to transmit (T) and receive (R) simultaneously two waves of orthogonally linear polarizations (LP), either at the same or two different frequencies. It can also be designed to transmit and/or receive two waves of the same linear polarization at two different frequencies with a single input port. There are also many possible designs for a single element to transmit or receive a circularly polarized (CP) wave of either the right-hand (RH) or left-hand (LH) sense, but not simultaneously.
The task of producing a microstrip antenna system which is capable of transmitting and receiving circularly polarized waveforms has been alleviated, to some degree, by the following U.S. Patents, which are incorporated herein by reference:
U.S. Pat. No. 4,379,296, issued to Farrar et al on Apr. 5, 1983; PA0 U.S. Pat. No. 4,367,474, issued to Schaubert et al on Jan. 4, 1983; PA0 U.S. Pat. No. 4,386,357, issued to Patton on May 31, 1983; PA0 U.S. Pat. No. 4,040,060, issued to Kaloi on Aug. 2, 1977; PA0 U.S. Pat. No. 29,296, issued to Krutsinger et al on July 5, 1977; PA0 U.S. Pat. No. 4,191,959, issued to Kerr on Mar. 4, 1980; PA0 U.S. Pat. No. 4,489,328, issued to Gears on Dec. 18, 1984; PA0 U.S. Pat. No. 4,130,822, issued to Conroy on Dec. 19, 1978; PA0 U.S. Pat. No. 4,197,545, issued to Favloaro et al on Apr. 8, 1980; PA0 U.S. Pat. No. 4,242,685, issued to Sanford on Dec. 30, 1980; PA0 U.S. Pat. No. 3,757,344, issued to Pereda on Sept. 4, 1973; and PA0 U.S. Pat. No. 4,078,237, issued to Kaloi on Mar. 7, 1978.
U.S. Pat. Nos. 4,379,296; 4,367,474; 4,386,357; 4,040,060; and 4,078,237 disclose patch antennas which include shorting pins. U.S. Pat. Nos. 29,246; 4,191,959; 4,489,328; 4,130,822; 4,197,545; 4,242,685; and 3,757,344 disclose patch antennas with slots therein.
A further development in the field of microstrip antenna technology is disclosed in the U.S. Patent Application of Dr. Yuen T. Lo and Mr. Bao F. Wang entitled "Dual Frequency Microstrip Antenna", Ser. No. 771,529 filed Oct. 21, 1985, the disclosure of which is incorporated by reference. The dual frequency microstrip antenna includes a single element patch which is capable of dual frequency operation, and used shorting pins and/or slots placed on the patch to vary the ratio of the two band frequencies.
While the references cited above are instructive, there remains a need to provide a microstrip antenna system which is capable of simultaneously transmitting and receiving circularly polarized waves. The present invention is intended to satisfy that need.